(a) Technical Field
The present disclosure relates in general to a method for compensating the nonlinearity of a resolver for hybrid and fuel cell vehicles. More particularly, it relates to a method for compensating the nonlinearity of a resolver to control a motor in hybrid and fuel cell vehicles, thereby stably controlling the motor current during high-torque and high-speed operation.
(b) Background Art
A hybrid vehicle using an engine and a drive motor is a vehicle which is driven by the drive motor during initial start-up and then driven both by the power of the engine and the power of the motor when the vehicle is moving above a predetermined speed, thus improving fuel efficiency and reducing exhaust gas.
A fuel cell vehicle is a vehicle equipped with a fuel cell stack, in which hydrogen supplied to the fuel cell stack is dissociated into hydrogen ions and electrons by a catalyst of a fuel electrode (anode), wherein the hydrogen ions are transmitted to an air electrode (cathode) through an electrolyte membrane, and oxygen supplied to the air electrode reacts with the electrons transmitted to the air electrode through an external conducting wire to produce water and electricity, thereby operating a drive motor.
Hybrid and fuel cell vehicles both employ a motor for driving the vehicle and an inverter system for driving the motor.
In particular, a resolver for detecting the speed of the motor and the angle of a rotor is employed in hybrid and fuel cell vehicles, where the detection and the failure detection by the resolver is regarded as one of the most important factors in motor control.
A configuration of the inverter system used in hybrid and fuel cell vehicles is described briefly with reference to FIG. 1.
A battery 10 is connected to an inverter 30 by a main relay 20, the inverter 30 is electrically connected to a motor 40 (e.g., permanent magnet synchronous motor), and the motor 40 is equipped with a resolver 50, which is a type of rotation angle detection sensor for detecting the absolute position of a rotor and transmitting the detection signal to the inverter 30.
The inverter 30 preferably includes a power module 31 (e.g., IGBT), which transmits electrical energy between the battery 10 and the permanent magnet synchronous motor 40, a DC link capacitor 32, which absorbs the ripple component of DC voltage caused by the operation of the inverter 30 to prevent the ripple component from being transmitted to the battery 10, a DC link voltage sensor 33, which measures the DC voltage of the inverter 30, i.e., the voltage at both ends of the DC link capacitor 32, to be used to control the inverter 30, a DC link voltage sensing circuit 34, which processes the output of the DC link voltage sensor 33 to have a magnitude capable of being input to an AD converter and, at the same time, prevents the occurrence of a voltage measurement error due to noise, etc., a current sensor 35, which measures the alternating current of the inverter 30 to be used to control the inverter 30, a current sensing circuit 36, which processes the output of a current sensor in a current sensor module to have a magnitude capable of being input to the AD converter and, at the same time, prevents the occurrence of a current measurement error due to noise, etc., a CPU 37, which is equipped with a software for controlling the inverter 30 and controls the overall operation of the inverter 30 using measured physical parameters, and a control/gate board 38 equipped with the above-described circuits and components used to control the inverter 30.
Preferably, the resolver 50 is used as a position sensor for detecting an accurate position of the motor rotor to accurately control the motor 40 by means of the inverter 30.
Accordingly, when the accurate position of the motor rotor is not suitably detected, it is difficult to satisfy a driver's demand torque and the controllability of the motor may be lost. Therefore, it is necessary to establish a coordinate system for the vector control of the motor in synchronization with rotor flux position and, for this purpose, it is necessary to read the absolute position of the motor rotor. Accordingly, the resolver is used to detect the absolute position of the rotor (i.e., rotation angle of the rotor).
Preferably, the resolver is generally composed of two elements. That is, the resolver is preferably composed of a rotor and a stator, like the motor. The rotor of the resolver is attached to the rotor of the motor, and the stator of the resolver is attached to the stator of the motor.
Therefore, the resolver rotates by receiving an excitation signal of 10 KHz generated from a resolver-to-digital converter (RDC) of the inverter to deliver a sine wave and a cosine wave to the RDC, demodulates the excitation signal component (10 kHz) from the sine wave and the cosine wave, and detects the position of the motor rotor.
Accordingly, each phase of the rotor is accurately measured by the resolver, and the RDC including a synchronous rectifier for rectifying the measurement value and a voltage control oscillator (VCO) for outputting the rectified voltage at a desired oscillation frequency transmits the measured phase of the rotor. Therefore, it is possible to accurately control the motor speed and the motor torque required for the vehicle operation.
As shown in FIG. 2, the ideal position information of the motor rotor should have linearity. However, the position information of the motor rotor detected by the resolver has nonlinearity which is out of the ideal position information. It is believed that the nonlinearity is may be caused by the hardware characteristics of the resolver itself, while there is a difference in degree.
In the event of an error in the resolver due to the nonlinearity, the hybrid function may not work due to an error in the inverter during maximum torque/power operation at low speed and high speed, the stability of the current control may be reduced during high-torque and high-speed operation of the motor, and an increase in ripple (loss) may be caused by an increase in asymmetry of the motor phase current.
In other words, when an error occurs in the position information of the motor rotor due to the nonlinearity of the resolver, the control of the motor current by the inverter may become unstable during maximum torque operation at low speed. Further, when measuring the speed used in a motor control algorithm, it is impossible to measure an accurate speed, which may make the control of the motor current unstable during maximum power operation at high speed.
Accordingly, there is a need in the art for methods for compensating the nonlinearity of a resolver to control a motor in hybrid and fuel cell vehicles.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.